the way the curve is, and ground is zero, the lowest point would be -7, but we want the lowest point to be 1.5, so wouldn't we have to raise the curve up 8.5 ?
so far we have : height = 7 sin (πt/8) + 8.5

since you did not state where you want the bottom of the wheel to be at a given time, I cannot find the phase shift

As the wheel slows down, the period would become longer, and the sine curve would be stretched horizontally, nothing happens vertically.